[sdiy] Fixing the aftertouch in a Yamaha DX11?

[cheater cheater]

Hey guys,
the after touch in this one is completely dead. When I use it as a mod
source, it just outputs random gibberish.
I have two, one back in mainland Europe, and both have dead aftertouch!
The metal strips (so, the terminals of the variable capacitor) seemed
oxidized in both.
Has anyone got an idea how where to get the parts or how to fix it?
I'm not sure whether it could still be available at all!
I am currently in London and would love to find a place that offers the part.

NB: I bought this one for 37 because it was sold as 'broken'. Reason:
after booting up, display showed 'Please replace battery'...

Cheers!